Bulletin of the American Physical Society
2020 Fall Meeting of the APS Division of Nuclear Physics
Volume 65, Number 12
Thursday–Sunday, October 29–November 1 2020; Time Zone: Central Time, USA
Session LJ: Mini-Symposium: Nuclear Physics from Effective Field Theory and Lattice Field Theory IV |
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Chair: Amy Nicholson, UNC |
Saturday, October 31, 2020 10:30AM - 10:42AM |
LJ.00001: Next-to-next-to-leading order $\Delta$-full and $\Delta$-less chiral effective field theory in harmonic oscillator basis Aaina Bansal, Ragner Stroberg We regulate chiral effective field theory (EFT) potentials up to next-to-next-to-leading order (NNLO), with and without intermediate $\Delta$-excitations, directly using momentum space discrete variable representation for finite harmonic oscillator basis. We extend the method, previously developed for pionless effective field theory, to include additional pion-exchange terms between two nucleons ($NN$) and three-nucleons ($3N$) in chiral EFT. The key benefit of this approach is the ensured ultra-violet (UV) convergence without the need of starting from a large enough model space to capture the tail of conventionally employed momentum space regulators. We tailor the potentials to three different model spaces, $N = 6, 8$ and $10$, with oscillator spacing tuned to obtain 450 MeV and 500 MeV UV cutoffs for each model space. The low-energy coefficients of the $NN$ and $3N$ EFT interactions are adjusted to reproduce the low-energy $NN$ phase shifts and the triton binding energy, respectively. We compute the ground state energies of nuclei with mass number $A = 2,3$ and $4$, as proof of principle calculations for this framework. Further, we compute the ground state of $^{16}$O and $^{40}$Ca nuclei and study their infrared convergence with increasing many-body model space. [Preview Abstract] |
Saturday, October 31, 2020 10:42AM - 10:54AM |
LJ.00002: {\it Ab initio} calculations of low-energy nuclear scattering using a L{\"u}scher-like method Xilin Zhang {\it Ab initio} nuclear structure calculations that compute nuclear static properties based on underlying nucleon interactions have now progressed to studying medium-mass nuclei. However, first-principle calculations for nuclear scattering and reactions are still limited to light systems. A method suitable for heavier nuclei would be very valuable in studying scattering and reactions with astrophysical relevance and for the success of the coming FRIB program that will focus on unstable nuclei near drip lines. In this talk, I will present my recent development of such a method. It modifies the so-called L{\"u}scher method, used in Lattice QCD for computing hadronic scattering, to compute nuclear scattering. The key idea is a computational experiment: realizing the trapping of nucleus-nucleus or nucleus-nucleon systems in harmonic potential well within the {\it ab initio} structure calculations, and then extracting scattering information from the computed discrete energy levels. I will discuss the formalism and report encouraging results from my collaboration with {\it ab initio} groups on computing neutron--alpha and neutron--Oxygen-24 scattering phase shifts. I will end with a brief discussions on future developments. [Preview Abstract] |
Saturday, October 31, 2020 10:54AM - 11:06AM |
LJ.00003: Scattering phaseshift formulas for moving frames in elongated boxes Frank Lee, Andrei Alexandru We derive L\"{u}scher phaseshift quantization conditions for two-particle moving states in boxes elongated in one of the dimensions. Boosted states in three different directions, (0,0,1), (1,1,0), and (1,1,1), are considered. The formulas are compared with those in cubic boxes. They are numerically validated in a simple model by solving the Schr\"{o}dinger equation on discretized lattices. The predictive power for the lowest partial wave in various irreducible representations is examined. Effects of higher partial waves are investigated by reverse-engineering the quantization conditions. The results can serve as a bridge between energy levels in finite volume and more sophisticated models for meson-meson and meson-baryon elastic scattering processes in infinite volume. [Preview Abstract] |
Saturday, October 31, 2020 11:06AM - 11:18AM |
LJ.00004: Recent results from nuclear lattice simulations Ning Li We determine new lattice interactions including two- and three-body interactions up to nex-to-next-to-next-to-leading order (N3LO) in chiral effective field theory. The low-energy constants are fixed by the 2N scattering phase shifts and Triton binding energy. We will present the neutron-proton scattering phase shifts, the binding energies of light- and medium-mass nuclei as well as the density profiles for some selected alpha-like nuclei. The results for the new lattice interactions are much better than those in our previous nuclear lattice simulations. [Preview Abstract] |
Saturday, October 31, 2020 11:18AM - 11:30AM |
LJ.00005: Symplectic Effective Field Theory David Kekejian, Jerry Draayer, Kristina Launey We explore the origins of symplectic symmetry, a dynamical symmetry that is commonly displayed in atomic nuclei, from the first principles of quantum field theory. We consider a simple Lagrangian that is an extension of the harmonic oscillator Lagrangian and show that the next approximation to the harmonic oscillator Hamiltonian is symplectic in nature. Our theory accurately predicts the coupling coefficient of the interaction, the time evolution of the dynamics, and in so doing reveals why symplectic algebraic models have historically proven to be so successful in describing nuclear systems. [Preview Abstract] |
Saturday, October 31, 2020 11:30AM - 11:42AM |
LJ.00006: Analyzing discretization effects in Nuclear Lattice computations Christopher Koerber Computations of physical systems must be independent of the basis they are performed in. In the case of Nuclear Lattice computations, this basis generally corresponds to a finite volume on a discrete lattice. However, because of computational costs and the complexity of nuclear forces, results of non-relativistic Nuclear Lattice computations with nucleons as degrees of freedom are frequently evaluated at finite lattice spacings. The topic of this talk is the analysis of finite lattice spacings effects on scattering data in a two-nucleon system described by a contact interaction mimicking nuclear forces. Furthermore, for such contact interactions, a modified infinite-volume formalism considering finite discretizations is presented. This formalism enables the control of discretization effects in two-fermion systems up to numerical precision--which can be used to prepare computations of unitary fermions. [Preview Abstract] |
Saturday, October 31, 2020 11:42AM - 11:54AM |
LJ.00007: An Effective Field Theory Approach to Rotational Bands in Odd Mass Nuclei Ibrahim Alnamlah, Eduardo Antonio Coello Perez, Daniel Phillips We present the low-energy rotational bands resulting from the coupling of a fermion to a deformed axially-symmetric nucleus within an effective field theory (EFT). The low-energy degrees of freedom of the deformed nucleus result from the breaking of rotational symmetry and enter the Lagrangian as time derivatives of the orientation angels of the symmetry axis. In the body-fixed frame they couple to the total angular momentum of the additional fermion. To first order in rotor angular velocity this coupling is the well-known Coriolis coupling. The resulting Hamiltonian is systematically improved to higher orders in rotor velocity. The result is a systematic organization of terms that appear in classic formulae of the particle-plus-rotor model [1]. (See also the recent [2].) We apply our organization of the problem in different nuclei, and assess its validity by examining the residuals at each order in the expansion and discuss how the breakdown scale of the EFT manifests itself in such an analysis. [1] A. Bohr and B. R. Mottelson.Nuclear Structure. Vol. II: Nuclear Deformation. (W. A. Benjamin, Read-ing, Massachusetts, USA, 1975). [2] T. Papenbrock and H.A. Weidenm uller. In:(May2020). arXiv:2005.11865 [nucl-th]. [Preview Abstract] |
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